How can the brain adapt to new environments while protecting its architecture from modification from the continual bombardment of undesirable information? The goal of the present proposal is to clarify how low-level sensory systems solve this stability-plasticity dilemma. Until recently, it was thought that low-level sensory systems were rigid and, therefore, resistant to environmental changes, and that only with persistent and focused attention on primitive features can these systems be modified. However, recently a series of studies have indicated that the low-level visual system is significantly more plastic than previously thought. Performance improvement on a sub-threshold, task-irrelevant feature occurred without attention to that feature (Watanabe et al, 2001,2002; Seitz & Watanabe, 2003). If attention does not gate learning, then what protects the sensory systems from undesirable modification? To address this question, we propose a series of psychophysical experiments to investigate how plasticity is gated in low-level sensory systems. These experiments will explore different aspects of learning and plasticity in the early sensory systems; the associability of learning, depth of processing required for learning, dynamics of learning, interference of learning, and learning across the same or different pathways or sensory modalities. Successful clarification of these gating mechanisms for learning will greatly contribute to our understanding of how the stability-plasticity dilemma is solved in low-level visual stages. [unreadable] [unreadable]